Juvenile diabetes mellitus or insulin dependent diabetes mellitus outranks all endocrine disorders in incidence, morbidity and mortality. The risk of its complications and mortality, however, does not appear to have changed in the last 30 years. The cause of the disease is still unknown, but genetic predisposition, viral agents and autoimmunity all appear to be important. Recently, we used cultured human insulinoma cells as model pancreatic islet cells to demonstrate circulating autoantibody to sensitized lymphocytes in patients. On the basis of our finding, we further proposed to study the specificity of the test and its duration to the diseases. We also proposed to study a possible linkage between the viral insult and the development of autoimmunity. So far our findings strongly indicated the susceptibility of the disease is linked to the alteration of immune response in patients. We also have conducted a paralleled animal experiment which so far confirmed the beta cell injury was caused by autoaggression of immunocytes in susceptible animals. These informations will provide a better understanding of the disease as well as preventive measures in the future.